Temporal variations in heterotrophic mesophilic bacteria from a marine shallow hydrothermal vent off the Island of Vulcano (Eolian Islands, Italy)

The fluctuations of the total microbial abundance, the culturable heterotrophic bacterial population, and the composition of heterotrophic bacteria were investigated in relation to environmental parameters in a shallow, marine hydrothermal vent off the Island of Vulcano (Eolian Islands, Italy). Standing stock dynamics were studied by measuring the total population of picoplankton by direct count and the population of viable heterotrophic bacteria in water and sediment samples collected monthly. The environmental factors most strongly linked to the total microbial abundance and heterotrophic bacterial populations were pH and H2S content in water and C/N ratio in sediment samples. The pattern of variation of microbial populations associated with water was different from those associated with sediment. Assessment of the qualitative composition of aerobic heterotrophic bacterial communities was based on 30 morphological and biochemical characteristics for each strain, Numerical analysis was used for an initial survey of the similarity among the isolates. The data were successively used to determine the structure and the metabolic potential of water and sediment bacteria. Metabolic properties varied between water-and sediment-isolated bacteria. Bacteria from water were structurally more diverse, and active in the use of carbohydrates, than those from sediment. Moreover, most of the sediment bacteria were able to grow at a high temperature (60 and 70 degrees C). The fluctuations of bacterial characteristics in relation to environmental parameters present an evident temporal variation in water, but not in the sediment habitat.